1. Field of the Invention
The present invention relates to a gain adjustment method, a gain adjustment circuit, and an optical disc device having the gain adjustment circuit. More particularly, the present invention relates to a gain adjustment method suitable for processing a wobble signal in a disk-shaped recording medium having wobbling grooves (guide grooves), a gain adjustment circuit for use therewith, and an optical disc device having the gain adjustment circuit.
2. Description of the Related Art
In the related art, in an optical disc device for recording predetermined data on a disk-shaped recording medium having wobbling grooves or for reproducing data recorded on a disk-shaped recording medium, predetermined laser light is irradiated onto the disk-shaped recording medium, the reflected light thereof is detected to generate a wobble signal or a land prepit signal, and on the basis of a control signal, such as the wobble signal or the land prepit signal, data are recorded or data are reproduced.
In particular, the reflected light from the disk-shaped recording medium is detected using a photodetector having two optically divided portions along the tangent direction of the tracks provided on the disk-shaped recording medium.
Then, two signals output from the photodetector are each gain-adjusted by a VCA (variable gain amplifier) circuit. The two gain-adjusted signals are input to a differential device, whereby a combined signal is generated. This combined signal is input to a wobble signal detection circuit and a land prepit signal detection circuit, whereby a wobble signal and a land prepit signal are generated respectively (refer to, for example, Japanese Unexamined Patent Application Publication No. 2002-117536).
When the gain is adjusted using gain varying means such as a VCA circuit, as shown in FIG. 5, a first detection signal s110 output from a photodetector is input to a first VCA circuit 210. Also, a second detection signal s120 output from a photodetector is input to a second VCA circuit 220. The first output signal s210 and the second output signal s220, which are each gain-adjusted, are output from a first output terminal 410 and a second output terminal 420, and, in addition, these signals are input to a detection circuit 300.
In the detection circuit 300, a first control signal s310 for controlling the first VCA circuit 210 is generated and also, a second control signal s320 for controlling the second VCA circuit 220 is generated. The first control signal s310 is input to the first VCA circuit 210 and also, the second control signal s320 is input to the second VCA circuit 220, so that feedback control of the first VCA circuit 210 and the second VCA circuit 220 is performed, making it possible to output the first output signal s210 and the second output signal s220 on which desired gain adjustment is performed. In FIG. 5, reference numeral 110 denotes a first input terminal, and reference numeral 120 denotes a second input terminal.